1. Field of the Invention
The present invention relates to a method and an apparatus for producing a fasciated yarn.
2. Description of the Prior Art
In fasciated yarn spinning, a fiber bundle delivered from a pair of front rollers of a draft means is introduced into an air nozzle and therein is false twisted by a vortex. During untwisting of the false twisted fiber bundle, part of the fibers in the fiber bundle entangle around a core portion thereof to form a fasciated yarn. Generally speaking, in order to obtain a good quality yarn, the fiber bundle has to be fed in the shape of a ribbon having a sufficient number of free-end fibers prior to being twisted. A free-end fiber is a fiber wherein one end thereof is embedded in the body of the bundle and the other end is free. By the application of a vortex, part of the free-end fibers are converted to wrap fibers which entangle around the resultant yarn.
In order to generate a sufficient number of free-end fibers, twisting of the fiber bundle in the nozzle inlet must be suppressed as much as possible to maintain the ribbon shape thereof. Therefore, a typical conventional air nozzle has a small channel in its fiber passage between the inlet portion and a large channel in which a vortex is generated. The false twist of the fiber bundle can be prevented to a certain extent from ascending to the inlet portion by the small channel.
Naturally, the twist-suppressing effect increases as the cross-sectional size of the small channel becomes smaller. However, a reduction of the size of the small channel causes insufficient suction of the air nozzle, which results in various problems, such as the generation of many flies, fiber wrapping on the roller surface, and the generation of less free-end fibers.
On the contrary, simply increasing the size of the small channel results in a decrease of the twist-suppressing effect. This drawback is augmented by the generation of ballooning, which disrupts the stable spinning operation and deteriorates the quality of the resultant yarn.
When ballooning occurs in the air nozzle, the false twist imparted to the fiber bundle easily escapes upstream toward the front rollers, and, as a result, a final twist remaining in the downstream region of the fiber bundle is insufficient for forming a strong yarn.
In an attempt to eliminate such drawbacks, there is disclosed in Japanese unexamined patent publication (Kokai) No. 52-63439 an air nozzle having a bent large channel. In this air nozzle, the fiber bundle tends to deviate from the center axis of the large channel and the rotation thereof is braked by contact with the inner wall of the large channel. As a result, the total twist imparted to the fiber bundle is insufficient, and the resultant yarn has a looser structure than does a conventional yarn.